Flame retardant molded composition which incorporates a poly[N-(bromophenyl)maleimide-co-styrene-co-N-phenylmalemide] copolymer

ABSTRACT

A moldable composition which comprises a novel random N-(halogenated phenyl)maleimide-containing copolymer and a flame-retardant synergist is disclosed. The molded composition exhibits at least a 94V-1 classification when tested in accordance with Underwriters&#39; Laboratories Inc. Test Method UL94.

This is a division of application Ser. No. 685,355, filed Dec. 24, 1984,now U.S. Pat. No. 4,609,711.

This invention relates to polymers.

In one of its more specific aspects, this invention relates to amoldable polymer composition which, upon molding, exhibits excellentnonflammability properties.

The present invention provides a random N-(chlorinated or brominatedphenyl)maleimide-containing copolymer and a composition which comprisesa flame retardant "synergist" in combination with the random styreniccopolymer. The composition, upon molding, exhibits at least a 94V-1classification when tested in accordance with Underwriters' LaboratoriesInc. Test Method UL 94.

According to this invention there is provided a moldable compositioncomprising a random copolymer comprised of the following recurringunits: ##STR1## wherein R represents --H, --CH₃, or --CH₂ CH₃ ; each R¹separately represents --CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --OH,--NH₂, --OCH₃, --CO₂ H, --CONH₂, or --CON(CH₃)₂ ; each R² separatelyrepresents --H or --CH₃ ; R³ represents a C₁ to C₄ alkyl group or##STR2## R⁴ represents --Cl or --Br; x represents an integer of from 0to 3; and, wherein y represents an integer of from 1 to 3; and, aflame-retardant synergist.

Also, according to this invention there is provided a method forproducing a molded article which comprises (1) blending a randomcopolymer comprised of the following recurring units: ##STR3## wherein Rrepresents --H, --CH₃, or --CH₂ CH₃ ; each R¹ separately represents--CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --OH, --NH₂, --OCH₃, --CO₂ H,--CONH₂, or --CON(CH₃)₂ ; each R² separately represents --H or --CH₃ ;R³ represents a C₁ to C₄ alkyl group or ##STR4## R⁴ represents --Cl or--Br; x represents an integer from 0 to 3; and, wherein y represents aninteger of from 1 to 3; and, a flame-retardant synergist; and, (2)molding the resulting blend.

According to this invention there is also provided a random copolymercomprised of the following recurring units: ##STR5## wherein Rrepresents --H, --CH₃, or --CH₂ CH₃ ; each R¹ separately represents--CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --OH, --NH₂, --OCH₃, --CO₂ H,--CONH₂, or --CON(CH₃)₂ ; each R² separately represents --H or --CH₃ ;R³ represents a C₁ to C₄ alkyl group or ##STR6## R⁴ represents --Cl or--Br; x represents an integer of from 0 to 3 and wherein y represents aninteger of from 1 to 3.

In a preferred embodiment of this invention, the total amount ofchlorine and/or bromine in the random copolymer will be within the rangeof from about 2 to about 16 weight percent, preferably, it will bewithin the range of from about 3 to about 12 weight percent.

In another embodiment of this invention the random copolymer is apoly[styrene-co-N-phenylmaleimide-co-N-(brominated phenyl)maleimide].

In another embodiment of this invention, the random copolymers can befoamed using any conventional method for foaming polymers such as, forexample, extruding the random copolymer in contact with a conventionalfoaming agent or impregnating the copolymer with a foaming agentfollowed by heating the impregnated copolymer above its glass transitiontemperature.

In another embodiment of this invention, the moldable compositioncomprised of a random copolymer and a synergist is employed as aflame-retardant blending component for thermoplastic resins; thecomposition serving as a flame-retardant for the resin. The compositionof this invention can be blended with any suitable thermoplastic resinincluding styrene/maleic anhydride, styrene/acrylonitrile, polyphenyleneoxide, styrene/N-phenylmaleimide, polyvinyl chloride, polycarbonate,polysulfone, polyarylate, polyester, polyamides and the like and theirmixtures. Impact modified resins are also suitable such as, for example,rubber modified styrene/maleic anhydride copolymer.

The amount of random copolymer-synergist composition employed whenblended with a thermoplastic resin is that amount effective to enhancethe fire-retardant properties of the thermoplastic resin upon molding ascompared with the flame-retardant properties of the thermoplastic resinin the absence of the random polymer-synergist composition. Typically,when employed as a flame retardant component, the randomcopolymer-synergist composition will be present in an amount within therange of from about 5 to about 50 weight percent based on the weight ofthe total composition.

The N-(chlorinated or brominated phenyl)maleimides which are suitablefor use as the first depicted recurring unit in the random polymers ofthis invention are not known to be commercially available. Suitable foruse are the N-(mono-, di- and tri-chloro- or bromophenyl)maleimides andinclude N-(4-bromophenyl)maleimide; N-(4-chlorophenyl)maleimide;N-(4-bromophenyl)citraconimide), N-(2,4,6-trichlorophenyl)maleimide andN-(2,4,6-tribromophenyl)maleimide. Bromine substituted maleimides arepreferred. The random copolymer will comprise from about 3 to about 75weight percent recurring units of this monomer. Example I demonstratesthe preparation of N-(2,4,6-tribromophenyl)maleimide.

In the practice of this invention, any suitable monomers can be employedto produce the second depicted recurring monomeric unit in the abovegeneral structure for the copolymer. Suitable monomers include: styrene,α-methylstyrene, α-ethylstyrene, methylstyrene, isopropylstyrene,t-butylstyrene, vinylbenzoic acid, vinyl phenol, vinyl analine,nitrostyrene, cyanostyrene, methoxystyrene, α-methyl-4-cyanostyrene,α-methyl-4-methylstyrene and the like, and their mixtures. Styrene isthe preferred monomer. The random copolymer will comprise of from about40 to about 95 weight percent recurring units of this monomer.

In the practice of this invention, any suitable monomers can be employedto produce the third depicted recurring monomeric unit in the abovegeneral structure. Suitable monomers include: N-methylmaleimide,N-phenylmaleimide, N-phenylcitraconimide,N-phenyl-3,4-dimethyl-maleimide, N-(4-cyanophenyl)maleimide,N-(4-hydroxyphenyl)maleimide, N-(4-aminophenyl)maleimide,N-(4-methoxyphenyl)maleimide, N-(4-benzamide)maleimide and the like, andtheir mixtures. N-phenylmaleimide is most preferred. And, although analkyl aryl substituted maleimide is preferred, maleimide may also beused. The random compolymer will comprise from about 1 to about 62weight percent recurring units of this monomer.

If the random copolymer of this invention is used to produce moldedarticles the number average molecular weight of the copolymers should beat least 30,000, preferably, 80,000 to about 500,000.

To produce a moldable composition of this invention the random copolymercan be conventionally blended with any suitable flame-retardantsynergist. The synergist will typically be employed in an amount withinthe range of from about 1 to about 10, preferably from about 1 to about5 weight percent of the total composition.

Suitable synergists include: antimony trioxide, antimony pentoxide,arsenic trioxide, arsenic pentoxide, zinc sulfate, zinc oxide, zincborate, bismuth oxide, molybdenum oxide, tungsten oxide, stannous oxideand the like, and their mixtures. The preferred synergist is antimonytrioxide.

Optionally, the molding composition can include other ingredients. Suchas extenders, smoke suppressants, antioxidants, reinforcing fillers,processing aids, pigments, stabilizers, mold release agents and thelike, for their conventionally employed purpose.

This invention is further demonstrated by the following examples.

EXAMPLE I

This example demonstrates the preparation ofN-(2,4,6-tribromophenyl)maleimide.

Into a reaction vessel were added and mixed 100 g. (0.303 mole) of2,4,6-tribromoanaline, 68.34 g (0.697 mole) of maleic anhydride, and5.16 g (0.379 mole) of zinc chloride.

The resulting mixture was heated at a temperature within the range offrom about 139° to 148° C. for about 2 hours.

The resulting reaction product was extracted with xylene, filtered andwater washed.

The xylene solvent was removed and the resultant productN-(2,4,6-tribromophenyl)maleimide was recovered at a yield of about 94%.

EXAMPLE II

This example demonstrates the preparation of a copolymer of thisinvention which contains recurring units of styrene, N-phenylmaleimideand N-(2,4,6-tribomophenyl maleimide).

Into a one-gallon stirred reactor were charged 2367 g of methyl ethylketone, 361.4 g of styrene, 528.2 g N-phenylmaleimide and 124.56 g ofthe N-(2,4,6-tribromophenyl)maleimide produced, using the procedure ofExample 1.

About 0.83 g of benzoyl peroxide was added to the reaction mixture andthe mixture heated to 75° C.

The resulting polymerization reaction was allowed to proceed for fivehours, and then 5 g of butylated hydroxytoluene ("BHT") were added.

The copolymer was recovered by precipitation from methanol, filtered,washed with methanol and dried under vacuum.

The recovered random copolymer was found to contain 61% N-phenylmalemideand about 7% tribromophenyl maleimide (4.1% bromine).

The copolymer was found to have a glass transition temperature of 228°C. (by Differential Scanning Calorimetry "DSC"), a number averagemolecular weight of 124,000 and a weight average molecular weight of248,000 as measured by gel permeation chromotography using polystyrenestandards.

EXAMPLE III

This examples demonstrates the preparation of a copolymer of thisinvention which contains recurring units of α-methylstyrene,N-phenylcitraconimide and N-(2,4,6-tribromophenyl maleimide).

Into a one-gallon stirred reactor is charged 2367 g of methyl ethylketone, 313 g of α-methyl styrene, 577 g of the N-phenylcitraconimideand 125 g of the tribromophenyl maleimide produced using the procedureof Example I.

About 0.8 g of benzoyl peroxide is added to the reaction mixture and themixture is heated to 75° C.

The resulting polymerization reaction is allowed to proceed for fivehours, and then 5 g of BHT are added.

The copolymer, a poly(N-(2,4,6-tribromophenylmaleimide-co-α-methylstyrene-co-N-phenylcitraconimide terpolymer isrecovered by precipitation from methanol, filtering, washing withmethanol and drying under vacuum.

The resulting copolymer is then blended with about 4 weight percentantimony trioxide based on the total weight of the copolymer plus theantimony trioxide.

Next, about 45 weight percent of the resulting blend and about 55 weightpercent of polycarbonate is melt blended at 550° F. extruded andinjection molded to produce a molded composition of this invention.

EXAMPLE IV

The copolymer produced in Example 2 was melt blended at 550° F. with 4%antimony trioxide based on the weight of the total composition(copolymer plus synergist),. The resulting blend was molded and themolded blend was tested for flammability in accordance with UnderwritersLaboratories UL 94 (UL 94 Standard for Tests for Flammability of PlasticMaterials For Parts in Devices and Appliances, UL 94, third edition Jan.24, 1980).

In this UL 94 Vertical Burning Test, the molded copolymer test specimenwas supported from the upper end, with the longest dimension vertical,by a clamp on a ring stand so that the lower end of the specimen was 1"above the top of the burner tube. The burner was then placed remote fromthe sample, ignited, and adjusted to produce a blue flame 1" in height.The test flame was placed centrally under the lower end of the testspecimen and allowed to remain for 10 seconds. The test flame was thenwithdrawn, and the duration of flaming or glowing combustion of thespecimen was noted. If flaming or glowing combustion of the specimenceased within 30 seconds after removal of the test flame, the test flamewas again placed under the specimen for 10 seconds immediately afterflaming or glowing combustion of the specimen stopped. The test flamewas again withdrawn, and the duration of flaming or glowing combustionof the specimen was noted. If the specimen dripped flaming particles ordroplets while burning in this test, these drippings were allowed tofall onto a horizontal layer of cotton fibers (untreated surgicalcotton) placed one foot below the test specimen. Significantly flamingparticles were considered to be those capable of igniting the cottonfibers. The duration of flaming or glowing combustion of verticalspecimens after application of the test flame (average of 5 specimenswith 10 flame applications) should not exceed 25 seconds (maximum notmore than 30 seconds) and the portion of the specimen outside the clampshould not be completely burned in the test.

Materials which comply with the above requirements and do not drip anyflaming particles or droplets during the burning test are classified as"V-1". Materials which comply with the above requirement but dripflaming particles or droplets which burned briefly during the test areclassified as "V-2". A "V-0" rating is given to materials wherein theduration of flaming or glowing combustion averages less than 5 secondsunder the conditions specified above.

The results of the UL 94 testing was as follows:

    ______________________________________                                        Molded Composition of                                                                         UL 94 (5" × 1/2" × 1/8")                          ______________________________________                                        Example 2       V-0                                                           ______________________________________                                    

It will be evident from the foregoing that various modifications can bemade to this invention. Such, however, are considered as being withinthe scope of the invention.

What is claimed is:
 1. A random copolymer comprised of the following recurring units. ##STR7## wherein R represents --H, --CH₃, or --CH₂ CH₃ ; each R¹ separately represents --CH₃, --CH₂ CH₃, --CH(CH₃)₂, --C(CH₃)₃, --OH, --NH₂, --OCH₃, --CO₂ H, --CONH₂, or --CON(CH₃)₂ ; each R² separately represents --H or --CH₃ ; R³ represents a C₁ to C₄ alkyl group or ##STR8## R⁴ represents --Cl or --Br; x represents an integer of from 0 to 3 and wherein y represents an integer of from 1 to
 3. 2. The random copolymer of claim 1 in which R³ represents a hydrogen.
 3. The random copolymer of claim 1 being poly[styrene-co-N-phenylmaleimide-co-N-(brominated phenyl)maleimide].
 4. The random copolymer of claim 1 containing from about 2 to about 6 total weight percent of chlorine and/or bromine.
 5. The random copolymer of claim 1 containing from about 3 to about 12 total weight percent of chlorine and/or bromine. 